A few people are reporting this problem due to an old cache being loaded. From the installation instructions, here is the fix:

If you are upgrading from a previous version of Maven, you should remove your local plugin directory, specified by MAVEN_HOME_LOCAL/plugins. The default location for this is HOME/.maven/plugins

The next Maven release will absolutely recognise this and avoid the need to delete ~/.maven/plugins. I've also fixed the corruption of the cache that can occur by running two instances simultaneously.

here are the release notes...

The Apache Maven team is pleased to announce the release of Maven 1.0 RC2.

http://maven.apache.org/start/download.html

Maven is a Java project management and project comprehension
tool. Maven is based on the concept of a project object model (POM).
The intent of Maven is to make intra-project development highly manageable
in the hopes of providing more time for cross-project development.

RC2 is a release candidate for Maven 1.0. The main focus for this release was
- Remove a memory leak in long-lived and multiple project builds
- Reworking the internals for more maintainability while retaining full backwards
compatibility with RC1.
- Many other bugfixes

For a complete list of changes in the Maven core, see JIRA:
http://jira.codehaus.org/secure/IssueNavigator.jspa?reset=true&pid=10030&fixfor=10245

While no new features have been added to Maven's central architecture, RC2
includes all the latest releases of the plugins developed at Apache. Most
plugins include bugfixes and new functionality since the RC1 release.

In addition, the following plugins have been added to the release:
- announcement: generates templated release announcements for a project
- aspectwerkz: Aspectwerkz integration
- caller: A goal interface for Maven plugins
- dashboard: A report plugin that aggregates reports from multiple projects
- javacc: generates code based on user-supplied Javacc/JJtree grammars
- jdiff: generates an api difference report between versions
- jetty: Jetty integration
- jira: generates a Maven report from JIRA
- multichanges: A report plugin that aggregates changes reports from multiple
projects
- nsis: generates a Windows Installer for your project using the Nullsoft
Installer System

The following plugins have had major upgrades since the last release:
- pdf: a complete rewrite now produces a much better PDF representation of
your project site.
- xdoc: Maven site's now have a new default look-and-feel and are more
customisable

For changes made to individual plugins since the last release, you can review
the release history at JIRA.

The following plugins are no longer distributed with Maven and must be downloaded
from an external source:
- cactus: download instructions at
http://jakarta.apache.org/cactus/integration/maven/index.html
- word2html, was40: download from
http://maven-plugins.sf.net

We hope you enjoy using Maven! If you have any questions, please consult:
- the FAQ: http://maven.apache.org/faq.html
- the Wiki: http://wiki.codehaus.org/maven/
- the maven-user mailing list: http://maven.apache.org/mail-lists.html

For news and information, see:
- Maven Blogs: http://www.mavenblogs.com/

- The Apache Maven Team